Design and optimise an SQL query for plotting markers on Google Maps

UPDATE: Just to clarify, I ONLY need the SQL query, I do not need any PHP or other code. I have a working solution already and just need to expand the SQL. I am a developer and will add your SQL into my existing code. I have a website that uses Google Maps to plot custom markers from a SQL database. The markers consist of store locations for ~10,000 currency suppliers in the UK. Visitors can enter their current location and see a list of currency suppliers within a 30-mile radius along with the supplier's corresponding exchange rate for a given currency. The problem I have is some suppliers have dozens of stores within a 30-mile radius of the search location which can look messy when the markers are plotted on the map. What I would like is to redesign the SQL query that finds these stores so that it does the following: 1) Find all stores within a 10-mile radius of the search location. 2) If there are multiple stores found for the same supplier, only return the first 5 for that supplier based on distance from the search location (i.e. the 5 closest stores). 3) Return a maximum of 50 results. The data is stored across three tables: Table 1 contains supplier information (name, website etc.). Table 2 contains marker information (including lat, long coordinates) for each store. Table 3 contains exchange rate information. The primary key in table 1 is a secondary key in tables 2 and 3. The final query must be fairly optimised (<1 second) as it will be placed on a medium-traffic website. I am open to changing the structure of one or more tables if necessary but would prefer not to.